Organic light emitting diodes (OLEDs) are useful in a variety of applications including use in watches, telephones, lap-top computers, pagers, cell phones, calculators, and the like. See, for example, U.S. Pat. Nos. 5,693,956; 5,151,629; 5,707,745; and 5,703,436 for conventional OLED devices, the disclosures of which are hereby incorporated herein by reference.
Conventional OLED display structures are built on glass substrates in a manner such that a two-dimensional OLED array for image manifestation is formed. Each OLED in the array generally includes overlying layers starting with a light transmissive first electrode formed on the substrate, an organic electroluminescent (EL) emission medium deposited over the first electrode, and a metallic electrode on top of the organic electroluminescent medium. When an electrical potential is placed across the electrodes, holes and electrons are injected into the organic zones from the anode and cathode, respectively. Light emission results from hole-electron recombination within the device.
Such OLEDs are often manufactured by first depositing the first transparent electrode on the substrate, and patterning same into electrode portions. Each electrode portion, by protruding or sticking up from the substrate, forms steps areas at edges thereof. The organic layer(s) is then deposited over the transparent electrodes and their steps.
Unfortunately, the organic layer(s) is susceptible to breaking down at these step areas, especially in view of the fact that the thickness of the organic layer(s) is often comparable to or thinner than the thickness of the transparent electrode layer. Such breakdown of the organic layer(s) at the step areas during fabrication or operation can cause significant yield loss which is magnified in weak or non-functional lines in the display. The yield loss may be more severe if the edge profile of an electrode at its step area(s) is steep and has sharp edge(s).
It is apparent from the above that there exists a need in the art for an improved OLED structure that is less susceptible to organic layer breakdown at step areas (i.e. at pixel edges), and a corresponding method of making such an OLED structure.
It is a purpose of this invention to fulfill the above-described needs in the art, as well as other needs which will become apparent to the skilled artisan from the following detailed description of this invention.